1. Purposes of the Invention
This invention relates in general to certain new and useful improvements in valve systems for controlling the flow of temperature regulated fluids, and, more particularly, to unique valve systems which permit diversion of temperature regulated fluids through a pair of fluid passages in the valve.
2. Brief Description of the Prior Art
In the processing of high viscosity, high temperature liquids, and especially thermoplastic and thermosetting polymer melts, it is necessary to pass the liquid plastic melt or other liquid material through filters. These plastic polymers contain many impurities which result in periodic clogging of the filters and, therefore, the necessary attendant cleaning of the filters. Accordingly, in the processing of these plastic liquid melts, whether monomeric or polymeric, two or more filters in parallel streams are often employed in a process such that one of the filters in one stream may be shut down for temporary cleaning with the other filter being operative in the other process stream.
Due to the necessity of two or more filters, valving arrangements are required in order to control the flow of the plastic liquid melt to the respective filters. Even moreso, it is well recognized that the liquid flow cannot be immediately shut off with respect to one filter and immediately diverted to another filter. Accordingly, the liquid flow is proportionally reduced to one of the filters with a proportional increase to the other of the filters until the flow has been completely diverted from one filter to another.
Presently, various forms of conventional plug valves, ball valves, spool valves, ram valves and the like are used in order to control the flow of a hot thermoplastic or thermosetting liquid melt. These valves are all of essentially conventional construction and are not very effective for purposes of controlling hot thermoplastic or thermosetting liquid melts, particularly of high viscosity, as for example, 1000 poise, and greater.
Notwithstanding the problems in controlling the fluid flow by means of valves, the valves as well as the fluid lines which carry the hot liquid plastic must be heat sealed. Moreover, the valves and fluid lines must be provided with a means for regulating the temperature of the hot thermoplastic melt during processing. Thus, for example, the various lines which carry the thermoplastic melt may be jacketed for receiving a suitable temperature maintaining or so-called "heat regulating" fluid. In addition, it is necessary to provide valves which contain jackets for receiving a heat regulating liquid to thereby maintain the liquid hot melt at a desired temperature during the processing.
Most of the conventional valves now used typically employ an outer jacket surrounding portions of the valve which receive a heat regulating fluid typically designed to apply heat to the valve and hence the plastic liquid melt passing through the valve. This arrangement has not proved to be too effective inasmuch as only the outer portions of the valve are heated.
Various forms of valves which have been used in the past are described in the Mayer et al. U.S. Pat. No. 3,817,668 and the Schippers U.S. Pat. No. 3,746,481. These patents describe valves which use gear wheels as a means of controlling the fluid flow, but constitute nothing more than conventional metering valves. However, here again, they have not proved to be fully effective in controlling the flow of hot liquids and particularly hot plastic liquid melts. Even moreso, they are not capable of operating as diverter valves.
U.S. Pat. No. 3,455,357 to J. Zink discloses a screen changer apparatus for extrusion machines. The screen changer device includes a shiftable plate which is capable of being shifted with respect to a pair of flow paths in order to divert flow during a screen changeover operation. However, this patent does not disclose an effective arrangement operable as a valve where an intermediate plate disposed between a pair of fixed plates is shiftable between such pair of plates in order to permit fluid flow through openings formed in the plates. In addition, the device is constructed so that venting must occur after changing a screen in order to permit effective operation of the device.
U.S. Pat. No. 3,727,767 to Itter et al. proposes a combination filter and valve arrangement in which two parallel filter-valve arrangements are employed. However, one of the major problems with this form of arrangement is that it is quite difficult to shut off the flow to one of the filters while maintaining the flow to the other of the filters. In addition, each filter-valve arrangement is quite complex in its construction, thereby necessitating almost complete disassembly of the valve-filter arrangement in order to clean the filter portion thereof. Notwithstanding the above, it has been found that this form of valve-filter arrangement has not been very effective in maintaining the liquid plastic melt at a desired temperature during the filtering thereof.
There have been many proposed dual filter arranagements in addition to that described in the Itter al. patent. For example, in British Pat. No. 1,168,063, removable filter pots are employed in the valve with stop cock or rotary slice valve arrangements. One of the principal problems in the aforesaid British patent, as well as the other prior art valve arrangements, is that after fluid flow is stopped through the valve, there is a standing amount of liquid polymer melt contained within the valve. This is highly undesirable inasmuch as the standing liquid melt tends to harden and thereby requires almost complete disassembly of the valve in order to clean the same. Most of the prior art valves do not afford any means for removing the remaining liquid melt in the valve after it has been turned to the "off" position, thereby stopping the flow of liquid polymer melt therethrough. In most conventional prior art valves, various forms of seals are used in the valve arrangement as in valves controlling the passage of low viscosity, low temperature fluids. However, when the valve is used for controlling the flow of a high viscosity, high temperature fluid, as for example, a hot thermoplastic liquid melt, this hot fluid has a tendency to cause deterioration of the seals in a relatively short time span. There has not been any valve arrangement which provides an effective seal which does not require a constant replacement.